Fluorine-18 undergoes beta-plus (positron) decay. What is the atomic mass of the resulting child isotope?

• A. 18
• B. 19
• C. 20
• D. 17

Answer: (A)

Verified step by step guidance

1. Understand that in beta-plus (positron) decay, a proton in the nucleus is converted into a neutron, emitting a positron and a neutrino. This process decreases the atomic number by 1 but leaves the mass number unchanged.
2. Identify the parent isotope: Fluorine-18 has an atomic number of 9 (since fluorine's atomic number is 9) and a mass number of 18.
3. Apply the effect of beta-plus decay: The atomic number decreases by 1, so the new atomic number is 9 - 1 = 8.
4. Determine the element corresponding to the new atomic number: Atomic number 8 corresponds to oxygen.
5. Note that the mass number remains the same during beta-plus decay, so the resulting isotope has a mass number of 18.